Manufacturing sheet-metal products of a predetermined shape by performing punching, bending, drawing, compressing and other forming operation on a sheet material, such as a steel sheet, usually involves several machining processes. When manufacturing a large quantity of such a sheet-metal product, a means is known for individually carrying out each machining process or stage in a single machining metal die set, while a workpiece is sequentially fed to the next stage to perform a new machining operation on the workpiece until the entire machining process is completed in the final stage. This type of machining die is generally called the progressive die. Since the progressive die can produce one piece of sheet metal product at every pressing stroke of the press, it has been widely used because of high efficiency.
The conventional type of progressive die, as described above, has various advantages, such as higher production rate, shorter delivery from the charging of workpiece through the completion of machining, less work-in-progress in the intermediate processes of the entire press machining, and volume production by a small number of operators. However, it has the following disadvantages. That is, since the progressive die has such a construction that a plurality of punch-die pairs are incorporated in a single metal die, the construction of the die becomes extremely complex, requiring high precision levels of die manufacturing technology, prolonged manufacturing time and high manufacturing cost.
When repairing a partly damaged die, or adjusting the die, it is necessary to disassemble the entire die. These operations are complicate and troublesome, requiring much time and labor. In a production setup to manufacture small quantities of a wide variety of products, if specially designed dies have to be prepared at every slight change in the shape and dimensions of workpieces, the increasing need for the so-called FMS production system in recent years could not be met.
To solve these problems, the present applicant filed earlier a patent application for an index-feed machining system having a simple construction and capable of easily performing partial adjustments. (Japanese Patent Application No. 121760/1989, 121761/1989, etc.) The present invention relates to a cassette changing apparatus, which represents a further improvement made on the basis of these improvement inventions and is intended to reduce substantially the retooling time of the index-feed machining system.
FIG. 1 is a perspective view illustrating an index-feed machining system to which this invention is applied. In FIG. 1, numerals 100-500 refer to machining units disposed on a base 1 at intervals of 2 P (P: a feeding pitch of workpiece), for example, in the feeding direction of a workpiece (not shown). These machining units 100-500 have punch/die pairs corresponding to a plurality of machining processes. Now, description will be made about the construction taking the machining unit 100 as an example. Numeral 101 refers to a machining unit proper formed into an essentially U shape having at the lower end an integrally formed dovetail 102, which is engaged with a dovetail groove 103 provided on the base 1 so as to allow the movement of the machining unit 101 to be adjusted in the feeding direction of the workpiece and to be constrained in the direction normal to the workpiece feeding direction. Numeral 104 refers to a movement adjusting device; 105 to a clamp device; 106 to a hydraulic cylinder provided on the upper end of the machining unit proper 101; and 107 to a position measuring device provided on the side surface of the hydraulic cylinder 106.
Numeral 108 refers to a cassette formed into an essentially U shape and having on the upper part thereof a punch or die (both not shown) in a vertically movable manner, and on the lower part thereof a die or punch (both not shown) mating with the punch or die described above; the cassette 108 being detachable. The cassette 108 is positioned by engaging positioning members 309 and 310, as will be shown with reference to a machining unit 300. Numeral 111 refers to a clamp screw. That is, the cassette 108 can be positioned at a predetermined location by fitting the cassette 108 to the machining unit proper 101 by means of a positioning member (not shown. Refer to numerals 309 and 310 in the machining unit 300.), and fixedly fitted to that location by tightening the clamp screw 111. After the cassette 108 is fixed, an operating lever (not shown) of the hydraulic cylinder 106 is connected to the vertically movable punch or die, as described above.
FIGS. 2A and 2B are diagrams of assistance in explaining the machining state of a workpiece. FIG. 2A is a plan view and FIG. 2B a cross-sectional view. Like parts are indicated by like numerals used in FIG. 1 above. In FIGS. 2A and 2B, numeral 2 is a workpiece that is intermittently indexed at intervals of P in the direction shown by an arrow in the figure. That is, the workpiece 2 is indexed in a gap between a pair of punch and die provided on the cassette 108 (the same applies to the other cassettes) in FIG. 1. In FIGS. 1, and 2A and 2B, the machining units 100-500 correspond with the machining process of pilot holes 3, the machining process of arc-shaped slits 4, and the first and third drawing processes.
The machining unit 100 has a punch and die for piercing the pilot holes 3, and guides (not shown) engaging with the pilot holes 3 at positions P in the feeding direction of a workpiece 2. Thus, every time the machining unit 100 is operated, the pilot holes 3 are sequentially machined and the guides are engaged with the machined pilot holes 3 to prevent the workpiece 2 from being unwantedly shifted in position so as to maintain machining accuracy.
The machining unit 200 machines arc-shaped slits 4, and the machining unit 300 performs the first drawing operation to form a cup-shaped projection 5 on the workpiece 2, and expands the width of the arc-shaped slits 4 to form into arc-shaped grooves 6. Moreover, the machining unit 400 performs the second drawing operations and the machining of flange holes 7, and increases the height of the projection 5. The machining unit 500 carries out the third drawing operation to form the projection 5 into a predetermined height. And then, trimming and other machining operations are carried out to obtain cup-shaped sheet-metal products of a predetermined size. Needless to say, positioning is performed for the machining units 200-500 by providing guides engaging with the pilot holes 3 to maintain predetermined accuracy.
The index-feed machining system of the aforementioned construction has a simpler construction than the conventional index-feed machining systems, and various advantages, such as the ease of manufacture and high-efficiency machining in production systems for producing a wide variety of products in small quantities. However, it has the following problems, too.
That is, when changing individual machining processes in the index-feed machining, the machining units 100-500 corresponding to the present machining processes, for example, have to be changed to machining units corresponding to new machining processes. In such a case, although the contents of machining units can be changed merely by changing the cassettes 108 fitted to the machining units 100-500, the operation of the index-feed machining system has to be interrupted while the cassettes in a plurality of machining units are replaced with new ones.
When the aforementioned cassettes are replaced with new cassettes, trial operations are needed to check for the degree of engagement between the punches and dies constituting cassettes, the state of machining the workpiece, dimensional accuracy. Furthermore, when the intervals of the new machining units are changed, positioning and feeding pitch and other adjustments have to be made. While these trial operations, adjustments and other retooling operations are performed, the index-feed machining operation on the workpiece must be discontinued. Needless to say, the index-feed machining system of the aforementioned construction has an effect of substantially reducing the time required for retooling, compared with the conventional index-feed machining system. In order to further improve productivity, however, it is necessary to further reduce the time required for retooling, thereby increasing the operation time of the index-feed machining system.